High-frequency electric arc



Aug.. ze 1924. 1,506,320

E. F. NORTHRUP HIGH FREQUENCY ELI-:cnn: Anc

Filed July 30, 1919 g4 ZIO/ZZ l?. IZWp/fzQ//glfzl minf. '1

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PatentedAug. 26, 1924.

UNITED STATES PATENT OFFICE.

EDWIN FITCH NORTHRUP, OF PRINCETON, 'NEW JERSEY, ASSIGNOR, BY MESNE AS- SIGNMENTS, TO AJAX ELECTROTHERMIC CORPORATION, 0F TRENTON, NEW JER- vI-IIGrl--FREQU'ENCY ELECTRIC ARC.

'Application filed July 30,

To all whom 'it may concern.'

Be it knoivn that I, EDWIN F. NORTHRUT, a citizen of the United States, residing at 30 Wiggins St., Princeton, in thev county ofv Mercer and State of New Jersey, have invented acertain` new and useful High-Frequency Electric Arc, of which the .following is a'specication. l l

My invention relates to arc lights which may be used for electric furnace or illuminating purposes.

The main purpose of my invention is'to apply a'high frequency electric current acting through aninductanc'e such that the resistance of the circuit due to variations in arc spacing, 'character and thickness of scum and skin on furnace metal surface, etc., becomes of relatively slight importance in the impedance of the circuit and' variation in the resistance' has little effect upon thema-intenance of the arc and the amount of current passing through it. This makes the arcless sensitive and requires less frequent adjustment of the arc. The quantity of current becomes to a much greater extent independent ofthe resistance and hence of the spacing of the arc. Freely oscillating current can be used to ladvantage for small heating installations and illuminating arcs thoughlarge furnace requirements place a high premium upon the use of a high' frequency generator.A

A further purpose is to use an oscillatory current where self-starting of the arc is desired, so that the peak'of the voltage may be available to start the. arc without neces- 'sity for maintaining so high an average voltage. l l

A further purpose is to apply a high frequency electric current through a plurality of circuits in multiple, each comprising one or more arcs and an inductance in series,

" with or without the use of the!` metal acted upon as an electrode.

invention relates to the. methods ofl^v` operation and also to the mechanism and connections by which the methods may be carried out. i

I have preferred to illustrate my invention, by but one' general form each from the electric furnace and lighting arts, selectingA forms which are practical, efficient and 1919. Serial No. 314,242.

highlydesirable, and which at the same time well illustrate the principles of my inven- Figure l is a diagrammatic view, showing someapparatus and illustrating the application of my invention to an electric furnace. Figure la Vis a diagrammatic view of a source of current supply.

Figure 2 is a horizontal section of the furnace offFigure l, intendedtoy be largely diagrammatic, taken upon line 2 2.

' Figure 3 is a side elevation of one form of my invention applied to an arc light.

Figures 4 and 5 are top plan views of Figure 3, but partly diagrammatic, showing.

two forms of connection thereof.

In the drawings similar numerals indicate like parts.

In the operation `of elect-ric furnaces of the arc-type, there has been considerable diliculty in heating the metal through the slag or other floating non-conducting and heat-insulating covering of the metal, leading to the use of smothered arcs and various special means for keeping the electrodes close to the metal.

There has also been considerable difficulty in maintaining a plurality of arcs in operation upon the metal surface in furnaces and in ladles because of the differences in spacing and it has been necessary to supply the arcs with 'an independent adjusting mechanism for each arc in order that its electrode or electrodes may be separately maintained in operativeposition. The same reliance 0f existing arcs upon a ycomparatively close range of electrodeA spacing for-successful starting of the arcs, which therefore require separate starting mechanisms.

So far as I am aware all users of commercial arcsfor either power orI lighting have avoided any considerable inductance in the circuits containing the arcs and I believe that I am the firstJ to provide an arc circuit for either purpose in which any considerable inductance is permissible as indestructive of the power factor or in which highpfrequency current is used in connection with inductance to secure a beneficial result from either.

Because of the excellent opportunity for operation has presented difficulty in the illustrationof the principles of my inven-'I 4 The leads 12, 12 from tion in cqnnection with' the ladle, and the utility of the same principles irl-electric furnaces, l have considered it unnecessal to show a furnace structure and havescon ned my metal heating illustration tothe ladle use v 1n 'Figure A-1 I have 'illustrated a source 10 of high frequency alternating current of an character, preferably a generator but whic may be o freely oscillatory form.

A convenient arrangement for vsecuring 4freely oscillatory high frequency supply is shown in Figure 1 in which alternating current leads A, A supply the primary of a. transformer T whosesecondary, charges a condenser'C. The condenser discharges through a gap Gr and the primary of an air transformer AT.

the secondary of the air transformer may feed the heating arcs or illuminating-arc directly, with or without capacity. 11 across them, or through another `air transformer as iniLFigure 8. lf'

the source be not freely oscillating, I prefer to place ua capacity 11 across the circuit 12,' i2'. The voltage may be high yor low as suits the particular installation and the views of the designer. l prefer to deliver alarge current at arelatively low voltage. My,

investigations lead me tol believe that an illuminating arc will i operate f successfully on volts effective or less and that tle voltage-for a-furnace may to advantage be three.

or four hundred volts. As. there is certainly a considerable range and myinvention does not depend upon the selection of any exact] voltage for its success, lv prefer not to indi-' cate any limits to the range.

l have indicated. loutV a single point of 'condenser application, preferringto lump the capacity here. The size of thecapacity is selected in such proportion to the inductance as to maintain a high power factor. Where no high frequency generator is used,

` the system by which the highl frequency current is provided will ordinarily contain condensers and may be made tcytake care ofthis factor.

The metal to be heatediis shown at 13'in i a broad and'shallow ladle 14, but may ob- ,f viously as indicated, loe-in .any1 electricfurnace, instead of in a ladle, if preferred, my-

invention .being applicable to both forms.

, The ladle is ordinarily shown asa poor l conductor, of heat and electricity and `is shown as comprising an outer metal shell 15, and a non-.conducting lining'16. Itis provided with :lifting ears 17, 17C,

I find' it--desirable to distribute a con siderable number of arcs uniformly spaced f overfthe surface of the metal'as best seen in Figure 2. Because l desire not to use the metal as an electrode, I form these arcs flVher it. is desired Y side of` the supply,-

in a number of pairs in series, with the pairs in parallel, some of which pairsl are represented in Figure 1, as at Y118, 19;.18, 19'; 182, 19?;'183,193 ;184,19; etc. Herelthe 18 series of arcs is formed between electrodes 20 and T0 the metal and the 19 series ofv arcs between, the met-al and electrodes 21. Electrodes 2( are connected with the side 12 of the supplj through articialor additional inducta'nces 22 and electrodes 21 are connectedgto the T5 side 12 of the supply, with orwithout inductances, as preferred.

With such frequencies as have been utilized heretofore in commercial `furnace and lighting equipments, any considerablev reac- 50 tance' hask been prohibitive `because, of its 'destructive effect upon'the power factor and it is only as the frequency is greatly increased that the inductances become advantageous.- The frequency is desirably thousands of cycles per second.

lt will be obvious that the inductance for the group can bev divided into two parts and placed iii-these two connections or be segregated in a single connection, as indicated, for gr'oulpsor for each pair, as preferred. i Y

For convenience'in adjustment of all; of the electrodes at one time, l show mechanism for "this purpose,I supporting all of the electrodesupon .a frame 23 which is intended to be typical of any form of support. or mounting for the velectrodes and which v is shown as conventionally adjusted in height by means of 'brackets 24 and screws 100 25. Provision for adjustment of all of the `arcs together by hand is not intended tolgether need not be as sensitive with the high frequency arc as with other arcs..

use the metal :is one of the 'electrodesg'it will be obvious that 'all of the-otherelctrodeswill 'be connected to onev side of the line `(and-,the metal'to the other side thereof and that separate inductances will beapplied in each of the circuits between the independent electrodes and their'A It is my purposeto make the inductances large enough so that the r`resistance of the arcs `will form but a relatively small partlzo of-v the total impedances of the individual, circuits, 'with the result that the .starting 'and' maintenance of the arcs will be suhstantially independent of tle'spacingof the individual electrodes'from the metal, yand 125'- that the arcs' formed from group of 'eleci trodes in their entirety to or from the metal will also be substantially independent of the spacing from the metal and that ythere will be practically the same arc-.formed in la@ each case, even though there be quite a con siderable difference in spacing. I note also that. where there is any decided difference in thespacing there will be a tendency to eren this because the additional current flowing Where the spacing is least will consumetha.' electrode more rapidly. maintaining an average spacing.

It Will-be obvious from the impedance diagram, that, if the inductance be 'high enough, the impedance will be substantially the same for considerable ranges of ohmic resist-ance.

Not only arel my arcs substantially independent of normal variations in spacing between the electrodes and the metal, but they are relatively free from interference by the character or thickness of skin or scum or slag or other non-conducting floating matter. Though this offers comparatively slight advantage in a ladle, Where the metal has already been purified and is Waiting for settling preliminary to pouring, it is of considerable ladvantage in application of my invention to electric furnaces in which melting or refining operations are to be performed.

I have discovered` that high frequency current produces an arc light of remarkable richness and brilliance and which is selfstarting at a lovv mean voltage., One form of this is shown in Figure 3. As this subject matter broadly comes Within the scope of my invention herein claimed I illustrate it and describel it in this application, though by reason of necessity for division from the heating form, I claim the invention as relating to arc lights in another application filed by me March 5, 1920, Ser. No. 363,455.

I hereshow an alternating current source of supply at 10 and condenser-f at 11 for a primary coiI 26, here'shown as helical, of an air transformer insulated at 27 and having a plurality of secondaries 28. These secondaries are shovvn here as comprising two turns each, butmay obviously. be of any number of turns that may be desired for the purpose of securing suitable voltage and current for operation ofthe arc. The form in the illustration is'intended to supply a heavy current at lovv voltage and the several coils 28 in parallel are connected respectively With collecting bars 29 and 30 connected with an arc light 31 Whose electrodes are shoyvn at 32 and 33. The arc light shown yis of the search light type and is provided with lenses,34.

The light is self-starting even on a mean voltage as low as 30 where the high fre` `quency supply is from condensers since the peak voltage of say 250 volts ensures starting.

As soar described, and as shown in Figure 4, no artificial inductance is applied, but` in Figure 5 I have shown aI form in which inductances 22 are used to reduce the dependence of the. light upon exact or delicate adjustment of the spacing of the electrode for continuance of operation, making the, light much more reliable, a 'feature which will be. Kappreciated in connection with the search light uses for which this are, on account of its great brilliance, is particularly suited. lVith either of the connections shown in Figures 4 and 5 automatic adjust ment of the spacing of the electrodes can lie provided.

In both the heating` and illuminating arcs it is highly desirable to maintain the` power factor of the, systems as nearly unity as possible. For a discussion of this I would refer to my Patents Nos. .1,286,391 and 1,286,395, both dated December 3, 1918.

Having thus described my invention, wha r.-

I claim as new and desire to secure by Letters Patent is l. A plurality of electrodes arranged to present |a. plurality of gaps for electric ares in combination with a source of high trequency alternating current supply therefor 'and an inductance in series with the parallel arcs.

2. A heating arc, 'comprising spaced electrodes in combination with a source of high frequency alternating current supply therefor and an inductance in series with thel are so proportioned that the ohmic resistance of the arc is a small factor only in the imped anceof the circuit.

. 3. A plurality of spaced electrodes for1nlng arcs, inparallel, in combination with a source of high frequency alternating current therefor, and an inductance in series With each'of the parallel circuits, so prtportioned as to render the ohmic resistance, ofthe arc a small factor onlyy in the impedance of each arc circuit.

4. Spaced electrodes adapted to the for mation of 'an arc,a high frequency alternal ing source of energy therefor. a capaet. across the alternating current source and an'added inductance in series with the elec trodes., A

5. Spaced electrodes adapted for the formation of a. plurality of arc circuits in multiple, .a common source of alternating current therefor, a capacity across the alternat ing current source and an inductance in series with each arc circuit.

6. A container for a bodyof metal to be. heated, an electrode in proximity to the,

metal space therein adapted for the formaa relatively small factor in the impedance ill) space of the arc and a capacity adapted towmainvtain the power factor of the source of electric current. l -7. `A. container for a body of metal to be heated` an electrode support vabove the metal therein, a pluralityof electrodes sup: ported thereby andxconnected td form circuits in multiple,vinea'ns for adjustinfr the 'support so as to space the electrodes from the metal, an inductance in'series with each electrode circuit and a, common source ofhigh frequency alternating electric current for all thefelectrode circuits.

8. A container fora body of metal -to be heated, an electrode support above the metal space therein, aplurality of electrodes supported thereby and connected to form cir-v i..uits in multiple, means for adjusting the support-'so as 'to space the electrodes from fthe metal, an inductance in series with each electrode circuit, a common source of high frequency alternatingelectric current for all;

the electrode circuits and means formaintalningl the power factor ofthe source of current,

i9.l A container for a body o'f metal to be V' heated, an electrode support above the space for the, metal therein, a 'plurality of elec.- trodes carriedV by said support,.adjusting means forv the support to space the .electrodes fromfthe metal, an inductance in series WithjeachA electrodel vcircuit so pro- 'reiti supply for the different circuits in"paral e i y10. A freely oscillatory. .supply in' combination with carbon Velec'- arc spacing and an 1n. ductance inseries in the arc and compris-l as compared with the ohmic .resistancev 4 quency electric* current supply,

` allel, each having an- .with the ohmicl resistance fof its-circuit a relativelyhigh part o f 4the impedance of the .of the arc a relatively smallt portioned as' to 'render the ohmic resistance factor in the impedance7 of the aro circuit and a .common source of high frequency. alternating' curelectlric current trodes forming an ing;

of the. arc, a relatively' large 'part of the impedance of the arc circuit.

11. An@ oscillatory source of high4 vfretion'with a plurality of, arccircuits in parinductance 1n its' circuit, the linductance forming .as compared --re'nt supply, i foran electrically conducting substance to be 12. A high frequency source of electric curin combination with a container heated, and-.an arccircuit connected with the supplytherefor, having, in series, 'two arcing points of separation from-said electrically conducting-body vtobe heated and v'an inductance. in 'series'with said arcs for1n-.. ing, as compared of the arcs, fa relatlvely large part of thev with the ohmic resistance impedance' ofthe circuit.

' adapted to the. formation of a plurality in combina-1 1a A ladi'jadapied to hold a, .body of metal to be heated therein, 'af plurality of pairs of electrodes therefor, 'the electrodes ofv a pair being allel, each electrode adapted to be spaced fromthe metal to bef'h'eated to formfan arc, added inductan'ce in series with each pair in series and the 'pairs in parand a liig'h frequency'source of alternating current supply for the pairs.

14. A. plurality vof' spaced electrode;y

o arcs in multiple, a high frequency alternatingsource of energy adapted to pass current through each arc and added inductance in the circuit relatively reducing the resistv ance of each arc to a small partn onlylof the impedance of the circuit.

A15. Spaced electrodes adapted for the formation of arc circuits in multiple, a com; mon source of alternating current therefor, a' capacity across the alternating current and added inducta'nce adapted to make the ohmic resistance of the arcs a 4small part only of the impedanceof thev system.` 41.6. A plurality of spaced electrodes adapted for the formation of a plurality .of arc circuits in multiple, a common source of high frequency .current therefor, and added induc'tance adapted to makeA ohmic resistance of the arcs represent a small part ,only of the impedance ofthe system.

the

` 17. A high frequency source of alternatnot parallel upon .the same? phase of curdue to variation [in resistance v make theimpedance ofthe circuitlargely independent of the resistance'. 1 the'variation -in 'current flow through electricl arcs. for furnace and 'illuminating purposes due to variation in resistance vi'fhiclrconsistsI in 19. The methodof overcoming adding inductance in 'seriesvwith the arc circuit to make the impedance o-f the circuit Vlargely independent of the vresistance, and

in applying a high frequency current to 'the circuit. 2O.- lhemethod` of making a commercial heating .or illuminating' arc self-starting, whichconsists in applying freely oscillat- I appropriate arc and'utilizing the peak of the voltage to start the are. v l 1 l 'EnWni riTcH Na'rnnnr.

'ing current lthereto havinga mean voltage' to the normal operation of the 

